The present invention is concerned with certain novel oxazino[5,6-c]1,2-benzothiazine, 6,6-dioxides and oxazino[5,6-c]1,2-thienothiazine 6,6-dioxides of the formula. ##STR2## which are useful oral prodrugs of the nonsteroidal antiinflammatory and analgesic oxicams from which they are derived.
The pertinent oxicams and their utility as antiinflammatory and analgesic agents are disclosed in U.S. Pat. Nos. 3,591,584; 3,787,324; 3,822,258; 4,180,662 and 4,376,768. U.S. Pat. No. 4,309,427 discloses certain ester derivatives of piroxicam, N-(2-pyridyl)-4-hydroxy-2-methyl-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide, and its N-(6-methyl-2-pyridyl) analog which are useful antiinflammatory agents, especially for topical administration. J. Med. Chem., 16, 44-48 (1973) discloses N-phenyl-4-acetoxy-2-methyl-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide as having moderate antiinflammatory activity while the corresponding 4-hydroxy compound had marked activity.
U.S. Pat. No. 3,923,801 discloses 5-methyl-3-aryl-2H,5H-1,3-oxazino[5,6-c]1,2-benzothiazine-2,4(3H)-dione 6,6-dioxides having inflammitory properties wherein the 3-aryl group is selected from phenyl and substituted phenyl. The compounds of this reference were prepared by reaction of the appropriate 2-methyl-4-hydroxy-2H-benzothiazine-3-carboxanilide 1,1-dioxide with e.g., a chloroformic ester, such as ethyl chloroformate, in the presence of an alkali metal base and contacting the resulting intermediate (III) ##STR3## wherein Ar is phenyl or substituted phenyl amd M.sup.+ is an alkali metal cation, with an acid to affect cyclization.